The present invention relates to an electrochromic solution, and more particular to an electrochromic solution containing a hydrazone compound. The present invention also relates to an electrohromic device manufactured with the hydrazone-containing solution, which is adapted to be used in an electrochromic rearview mirror assembly.
Glare is one of the troublesome factors when driving a vehicle. Many efforts have been made to solve the glaring problem. One of the most effective ways is to provide an electrochromic unit for the rearview mirror of the vehicle. The electrochromic unit deepens the color and thus reduces the reflection rate of the mirror accord to the degree of the glare, thereby minimizing the glaring effect. FIG. 1 is a schematic diagram showing a conventional electrochromic unit for use in a rearview mirror assembly of a vehicle to achieve the color-change purpose.
The electrochromic unit includes two glass substrates 11 and 12 positioned parallel to each other, and spaced apart by a distance of a micrometer-to-millimeter order. On each of the inner faces of the glass substrates, a transparent indium-tin-oxide (ITO) coating 13, 14 is provided as an electrode for electric conduction. The space 15 between the two glass substrates 11 and 12 is filled with an electrochromic solution and sealed with a material 16 inert to the electrochromic solution, e.g. epoxy. By applying a voltage across the ITO cathode and anode 13 and 14, the color of the electrochromic solution will change chemically. With the increase of the environmental light intensity, the voltage applied to the electrochromic unit increases, and the color of the mirror becomes darker.
In general, the electrochromic solution includes an anodic compound which undergoes a reversible color change when its valence state is altered due to oxidation, a cathodic compound which undergoes a reversible color change when its valence state is altered due to reduction, and a solvent which solubilizes the anodic and cathodic compounds but keeps chemically inert to the other constituents of the electrochromic solution. The electrochromic solution may optionally further includes an electrolyte material for enhancing the conductivity of the electrical current passing through the electrochromic solution. Please refer to U.S. Pat. Nos. 4,902,108, 5,679,283, 5,611,966, 5,239,405, 5,500,760 and 6,211,994B1 which are incorporated herein for reference, to realize examples of the anodic compound, cathodic compound, solvent and electrolyte material contained in conventional electrochromic solutions. In the prior art, the color change range of the electrochromic unit is from colorless to dark blue or dark blue-green, and the option of colors is quite limited. Further, when the voltage supply is removed, the color of the electrochromic unit is supposed to become colorless again. In practice, however, the color will not return colorless after a great number of color change cycles, but become pale yellow in stead. The rearview mirror thus looks somewhat dirty.
An object of the present invention is to provide an electrochromic solution which contains a photo-conductive compound as an anodic compound to enhance the color fixation thereof.
Another object of the present invention is to provide an electrochromic device which provides an alternative color option for a mirror.
A first aspect of the present invention relates to an electrochromic solution for use in an electrochromic unit for performing color change in response to a voltage applied to the electrochromic unit. The electrochromic solution includes at least one anodic compound, at least one cathodic compound and at least one solvent. The at least one anodic compound includs a hydrazone compound represented by the formula below: 
wherein
R1, R2, R3 and R4 are individually selected from a group consisting of hydrogen, alkyl containing 5 to 20 carbon atoms, alkenyl containing 2 to 20 carbon atoms, alkynyl containing 2 to 20 carbon atoms, and aryl containing 5 to 20 carbon atoms which are unsubstituted or optionally substituted with one or more ester, ether, aryl, amine, thioester, alkyl, alkoxy, alkene, alkyne, CN, F, Cl, Br, I and/or organometallcene functional group.
A second aspect of the present invention relates to an electrochromic device for use in a mirror for performing color change of the mirror in response to a voltage applied thereto. The electrochromic device includes a first transparent substrate; a second transparent substrate positioned substantially parallel to the first transparent substrate, and spaced apart from the first transparent substrate by a predetermined clearance to form a space therebetween; an electrochromic composition including a hydrazone compound, disposed in the space between the first and second transparent substrates; a seal disposed between the first and second transparent substrates for retaining the electrochromic composition in the space; and a pair of transparent electrodes provided on opposite surfaces of the first and second transparent substrates facing the space for providing the voltage for the electrochromic composition to perform color change.
A third aspect of the present invention relates to a hydrazone compound for use as a component of an electrochromic composition, represented by the formula (II): 
wherein
respective aryl rings are individually unsubstituted or optionally substituted with one or more ester, ether, aryl, amine, thioester, alkyl, alkoxy, alkene, alkyne, CN, F, Cl, Br, I and/or organometallcene functional group.